I personally just bought a few of those Nintendo Wii branded Sandisk cards, work with everything... bootmii/hbc/etc and arent really much more expensive than generic cards and avoids all the headaches.

What size is your card? according to the page I just linked to, SDHC cards are only supported in beta 9
and were only supported in later system menu versions. can you do an online update to the latest HBC? It would probably be best just to try another 1-2GB card.